Rereading your post, I see there's a potential case I haven't covered.
The approach I mentioned in the first post handles the case of many separate tasks in parallel being handled by your subcontractor. However, you might want to have all 6 of them working on the same task, to get it done in less time (and keep everyone busy). You can do that by assigning more than 100%, as seen here, where I've bumped the effort of Task 7 to be 6 days, and assigned the entire subcontractor resource to work on that:
